Telephone-exchange system



A. E. LUNDELL. TELEPHONE EXCHANGE SYSTEM APPLICATION FILED MAR. 25, 1918.

Patented Apr. 26, 1921.

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STA'lEfi ALBEN E. LTTNIDELL, OF NEVJ' YORK, N. Y.

PAN'Y, INCORPOREaTED, OF NEW YORK,

, ASSEGNDR TO VJESTEBN ELECTRIC COM- IN'. A COEPQBIATIUN OF NEW YORK.

TELEPHONE HJXGHANGE SYSTEM.

Application filed March 25,

T (all 10710112, it may concern:

Be it known that I, ALnnN E. LUYDELL, a citizen of the United States, residing at New York, in the county of Bronx, State of New York, have invented certain new and useful improvements in Telephone-Exchange tlysteins, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems in which manual lines provided with the usual manual station equipment, and automatic lines provided with the necessary substation apparatus for controlline automatic switches are ar 'anged to tcrminate in a common exchange, and to be served in part by the same switching and controlling apparatus employed therein in the extension of telephone connections.

The manual subscribers lines belongg'nia to an exchange of this character are arranged to terminate before operators positions, and the operator may be provided with suitable connecting means, such as cord circuits, whereby she is enabled to extend connections from calling lines to other lines of the same exchange whether of the manual or automatic type. The automatic subscribers lines terminate in line or finder switches at the exchange, and are provided with the usual substation calling dial by means of which the calling" subscriber con trols the operation oi. the selective switches to complete a connection to other lines of his own exchange.

More particularly, the arrangement of circuits and controlling apparatus involving the novel features of the present invention are embodied. in a telephone system including a plurality of private branch exchanges, each of which. is adapted to serve both manual and automatic subscribers lines in accordauce with the foregoing general de scription.

The object oi the intention consists in the provision oi trunking or connecting circuits in such a system whereby a (all originating, on a suhscrihers line individual to one private branch exchange may be extended to a second private branch exchange... and through the agency of switching devices thei'cat. extended to the desired line individual to the second exchange. The interexchange trunlrs are preferab y one-way connecting circuits and are available in either manual or dial subscribers stations. The

Specification of Letters Patent.

Patented Apr. 26, 1921.

1918. Serial No. 222,497.

outgoing end of these trunks terminates at the originating exchange in spring acks at an operators position, so that in case a manual subscriber desires connection with a subscriber in a distant private branch exchange, she may connect his line, by means of her cord circuit, to the interexchange trunk. The operator is equipped with calling mechanism in order to control the switches in the distant exchange over the trunk circuit. The outgoing end of the trunks also terminates at the originating exchange in theinultiple terminals of selector switches so that in case the subscriber of an automaticline wishes to converse with a subscriber individual to the second private branch exchange he is enabled to manipulate his calling dial, as when making; calls local to his own exchange, to extend his line to the distant excl'iange. By a further operation of his sending device he may then direct the switches in said exchange to connect his line with any subscribefis line terminating therein in a manner similar to that above described in connection with calls completed by an operator. V

A feature of the invention is the provision of a trunk circuit between private branch exchanges, in accordance with the above mentioned object, which normally remains in a non-talking condition during the calling period, and is arranged to transmit current impulses over its two conductors in series from the originating to the distant exchange, either under the control of a subscribers transmitter in the case of an automatic call, or the operators sending apparatus when. a manual line is being extended. After the connection has been completed and the called party responds, certain changes are elected whereby the trunk is automatizally converted troin'a condition adapted to the transmission of calling currents into one suitable for the transmission of voice currents.

.vinother feature resides in the provision oi": means whereby the operator in the origins-tin xchange is given sui'iervision of a called in a distant exchange through the agency o1": current chan es produced in the trunk circi' employed in establishing the connection between the exchanges.

Other objects of the invention will become ap *entfrom a consideration oi the following description and the appended claims.

In the drawings, Figure 1 shows a private branch exchange in which in ual station lines are associated with ope ors switching apparatus. and wlch calling dial station lines are terminated in automatic switches. This figure illustrates in particular only that portion or the exchange equipment involved in extending calling lines to outgoing connecting circuits leading to distant exchanges of the s rne general character, and accordingly the out going end of an interermhange trunk is shown terminating at an. operators position, and in the multiple of an 121118 switches; Fig. 52 shows a distant private branch exchange in which the incoiniing; end of the trunl: terminate toin a selector switch, gether with the circuits and operating mechanism arranged to be controlled over the trunk circuit by current impulses produced at the originating exchange: and u in: Q

0 shows the circuits and operating pa s adapted to complete the con called line.

It is believed a more thorough comprehension may be had of the advantageous trunking and supervision :t'eatures contemplated by the present invention b, a deteilcd description of the operation of the system in establishing a connection.

the manual substation whose line tcrinina-ites in the first exchange desires to converse with the subscriber at substation 300 whose line belongs to the second etchange. removing his "eceiver from the heel, ..is line is associated in any well-known manner with a cord circuit 101 at an operators position. The operator upon learning}; that connection is desir d with a line belonging to a distcnt Xchange, by means of her tel phone (not shown) then inserts the plug 102 of. cord circuit 101 in the jar-l; 103% of n outgoing trunk circuit 10 1c; eading; to such exchange. Upon the inserti n a the plug, a circuit is completed from ground, 106, sleeve of the plug and j clr. relay 107, to battery. Relay 107 energh-ics and at its right-hand arn aturc (noses 22 ch rit for displaying the supervisory lamp its lefthand armature, said relay also closes a circuit to place a guard ng ground upon the selector multiple to Hi. 109 to hold the seized trunk busy in the event a subscriber at an automatic substation such as substation. 110, attempts to make a call to the second exchange over the trunk 104;, 05. The following circuit is ct the sametime established to energize the stepping relay 111: battery, upper armature and back contact of relay 112, left-hand winding of low resistance relay 113, left-hand win-dine; oil relay 111, conductor 11 1, tip or the lack 0. new

' 103 and plug 102, upper right-hand winding of repeating coil 115, resistance 116, to

circuit extends from battery, winding of supervisory relay 117, resistance 118, lower right-hand winding, oi. repeating coil 115, ring; of plug 109 and jack 10, winding of relay 119, leitliand winding, of stepping relay 111, and to ground at the repeating coil 11' 1S above traced. The resistance oi his path is so high, however, that suiiicient rr nt does not flow to energize relay-s T and Consequently the supervisory amp 1120 remains extinguished and relay .19 at its armatures and contacts maintains the trunk 10%, telephonically disconnected from the operators cord circuit 1.01 and tie calling line.

13y attracting its armature the stepping 111 at the calling exchange completes called exchenge, Fig. 2, traceable from battcry, left-hand winling of relay 200, contact 201 of re a trunk conductor 105,

which by att -:actinp its left-hand armature prepares a *ircuit "tor the sending of impuises to the ope facing magnets of the first selector in the called exchange. .113 its righthend armature, this slow relay 205 places a break point in the circuit of the release magnet 2506, which circuit, as will hereinafter appear, is maintained open until he connection is taken down at the call- '1 eirchange. The operator having thus s ized the trunk circuit 10 1, 105, now presses oer calling lacy and operates the impulse sending device in accordance with the first digit of the called line. At ea :11 interruption by the s nder 123 of the pro viousiy traced circuit for the stepping relay 111, said relay retracts armeture to open the bridge at 'oss the outgoing end 01 the trunk 10%, 105, which in turn causes the repeating relay 200 to vibrate its armature correspondingly. At the first retraction oi? relay 5300, the "followin circuit is closed for the first selector primary magnet 530?, grounded armature and baclr contact of re lay 200, left-hand armature and front con tact of slow relay 205, left-hand armature and contact of relay 9 08, conductor 209, winding of slow relay 210, sideswitch arm (first position), winding of rotary stepping 207, to grounded battery.

Magnet 207 energizes and advances shaft 211, carrying brushes 212, 213 and 21 1, one rotary step. The slow relay 210 also energizes and at its lower armature closes a circuit leading over the side-switch arm 215 to the escapenient magnet 216. Said escapement magnet energizes preparatory to releasing: the side switch to its second position. it or each succeeding impulse transmitted over the trunk 10 1, 105 and repeated by the relay 200, the primary magnet 20'? rotates shaft 211 to finally bring the brushes 212, 213 and 21d into operative relation to the group of trunk terminals containing the terminals 217, 218 and 219 of a trunk leading to a linal selector switch. At the end of this series of impulses relay 200 remains energized and alter a brief interval theslow relay 210 releases its armatures to open the circuit of escapement magnet 216. Magnet 216 thereupon deenergizes and passes the side switch into position 2.

Vi hen the side switch arrives in its second position, a new circuit is completed for escapement magnet 21G, traceable from free pole of battery, winding of such magnet, contact and left-hand armature of release magnet 206, side-switch arm215 (second position), conductor 220, contact 232, to ground at the side-switch arm 221. The escapement magnet energizes and closes a circuitinclnding side-switch arm 222 (second position) for the secondary stepping magnet 223. This magnet upon energizing operates to step the positioned set of brushes 212, 213 and 21 1 onto the first set 01 terminals oi the chosen trunk group, and at the same time severe its own circuit. At the end. of this first step contact 232'isopened to thereby open the above traced circuit for the oscapenient magnet 216. If, however, the first trunk of the group is busy, there will be a ground present ontest terminal 219 thereof, and the escapement magnet is held energized. The secondary magnet thereupon proceeds to advance brushes 212, 213 and 21-l successively over the group until an idle trunk is found, at which time the escapement magnet deenern'izes and passes the side switch ,to position 3. V

The interexchange trunlr 1041, 105 has now been extended by means of a first selector'at the second exchange, 2, to an idle trunk, such as trunk 301, 302, 303, leadiug to a final selector switch, Fig. 3, of a cup or". selectors having access to the called line.

T he side switch of the first selector being in its third position. a circuit is completed as follows: ground, side-switch arm 22% (third position), brush 21 1, terminal. 219, conductor 303, right-hand armature and baclr. contact of the final selector release magnet 302:, side-switch arm 305 (first position), winding of relay 306, to battery. Re-

lay 806 energizes and at its outer righthand armature prepares a stepping circuit "for the final selector operating i'nagnets. At its left-hand armature said relay places a break point in the circuit of release magnet 30 1 to prevent a premature release of the switch. A ground is also applied from side switch arm 22s, the multiples 219 at other selectors, to prevent seizure of this trunk during the engaged period. The operator again manipulates her calling device 123 to send out the tens series of impulses, i *hich impulses operate as before to vibrate the armature of repeating relay 200. At the first retraction of such relay, the following circuit is closed for the i'inal selector primary stepping magnet- 307; ground, armature and back contact of relay 200, lefthand armature and contact of slow relay 205, left-hand armature and contact of relay 208. conductor 209, winding of slow relay 210, side-switch arm 225 (third position), conductor 22%, brush 212, terminal 217, conductors 301 and 308, outerarmature and contact of relay 306, side-switch arm 309 (first position), winding of magnet to battery. lnlagnet 307 energizes andadrances the final selector brushes 310, 311 and 312 through one rotative step. it the same time the slow relay 210 attracts its armatnres t capement magnet 313. This circuit leads from ground, upper armature and front contact of magnet 210, side-switch arm 227 (third position), brush 213, terminal 218, conductor 302, side-switch arm position), armature and contact of relay winding of magnet 313, to battery. ldagznet 3L energrizes preparatory adrancing: the side switch into its second posi tion. For eaclrsucceeding impulse o'li'the tens series the primary magnet 30'? isoperated to rotate the brushes 310, 311 and 312 into operative relation to the group of terminals containing those of the called line. At the termination of this series, relay 200 holds its armature attracted and after an interval the slow relay 210 deenergizes to open the circuit of escapement magnet 313, which on retracting allows the side switch to o o into second position. The relay 303 still remai s ener' 'ized over a circuit including its inner lt-hand armature and the second position contact of side-snatch arm 305. said arm 305 being; designed to engage its second contact before breaking connection with the first contact.

The switch is now in condition to receive the final series of impulses, which are sent out as abov des "ibed by the operators callina device 123. In response to the first impulse oi such series, and when the repeating; relay 200 retracts its armature, a circuit is established for the secondary net 316 from the grounded armature of reomplete a circuit for the eslay 200, over the path previously traced to the side-switch arm 309, and thence to the magnet 316 and battery. The slow relay 210 again energizes and closes a circuit "for escapement magnet 313, which leads from ground, the upper armature of relay 210, over the previously traced path of sideswitch arm 314-, now in position 2, to magnet 313 and battery. The magnet 313 energizes preparatory to releasing the side switch to position 3. At the same time a circuit is established for a slow relay 317, from battery, winding of such relay, sideswitch arm 318 (second position), and thence to ground at the upper armature of slow relay 210. For each impulse OT the final. series the magnet 316 advances the brushes 310, 311 and 312 one step over the group and finally brings them to rest on the terminals 319, 320 and 321 of the called subscribers line. Magnet 313 tie-energizes as before, and steps the side switch into third position.

Assume first that, when the brushes 310, 311 and 312 arrive on the terminals oi the called line, such line is already engaged. In this case, a non-selectable potential will be found on the test terminal 321, full potential having been removed or reduced in any well-known way in the event the line is busy as a calling line, or having been reduced by a circuit leading to ground at the left-hand armature and contact of a test relay 322 with sidcswitch arm 323 in third position, or to ground through the right-hand low resistance winding of relay with side-switch arm 323 in position l;

at some other final selector it the line is busy as a called line. In eithercase, the test relay 322 01" the switch shown does not receive su'flicient current through its high resistance winding to energize. lVith the side-switch now standing in position 3, the energizing circuits of relays 306 and 317 are opened. As soon thereafter as relay 317 releases its right-hand armature the relay 306 becomes inert, thereby closing a circuit tom battery, winding of release magnet 30%, left-hand armature and contact of relay 306, primary oitnormal contact 324; to ground. Release magnet attracts its armatures and releases the brushes 310, 311, 312 and the side switch to normal position. As the switch reaches its normal position primary olf-normal contact 32% is opened, which, however, does not occur until slightly after the closure of the normal contact 325. Hence the magnet 30% remains energized over the following circuit: battery, winding of magnet 30 1, left-hand armature oi relay 306, normal contact 325, resistance 326, front contact and right-hand armature of magnet 30 1, to the grounded third wire 303. When the final selector side switch reacl e its first position, a path is closed from the uctivcly transmitted back to the operasors telephone set. Being thus informed oi? the busy condition of the called line, the operator notifies the calling subscriber of such fact and removes the purg 102 from is. zlr The relay 111 thereupon deenergizes and opens the ln'idge across trunk conductors 10%1, 105, causing the repeating relay 200 to become inert. The slow relay 205 new deenergizes and closes the following circuit for the first selector release magnet 206: l; attery, wiming of magnet 206, conback contact and right-hand ductor '1- armature of relay 205, conductor 229, inner left-hand armature and baclr contact of relay 230, primary oil-normal contact 231 to ground. h'lagnet 206 thereupon operates to restore the selector and its associated side swi'cn to norms... hen brush 214E moves oil the terminal 219, ground is removed from wire 303 and the release magnet 304i retracts its armatures. lit the calling exchange the removal of plug 102 also severed the circuit of relay 107, which retracted its armatures to eflace the lamp 108, and to remove the busy condition from terminal 109. All apparatus is now in its normal tored position.

I however, the called line 300 is idle at the time connection is extended thereto, full potential is present upon the test terminal 321. lVhen the final selector sine switch passes to third position the test relay 322 is therefore energized over a circuit including its high resistance winding. Relay 322 at its right-hand armature closes a circuit as follows: battery, winding of escapement magnet 313, contact and armature of relay 315, side-switch arms 314 and 318 (third position), right-hand armature and low resistance winding of relay 322 to. ground. Relay 322 at its left-hand armature shunts out the high resistance winding, thus reducing the potential 0t test multiples 321 to make the called line non-selectable to other switches. A parallel circuit to the'one just traced for magnet 313 is also completed for the slow relay 317 as side-switch arm 318 goes to third position. Relay 306 at this time remains energized to hold the release circuit open over acircuit from battery, winding of such relay 306, its inner right hand armature and contact, contact and right-hand armature of the slow relay 317, to the grounded third conductor 303. The escapcment magnet 313 energizing in the above traced circuit applies ringing current to the called line as follows: ringing source 331, relay 315, inner armature and contact of magnet 313, side-switch arm 332, brush 311, terminal 320, over the loopo'f substation 300, terminal 319, brush 310, side-switch arm 231-323, to ground at the outerarmature ot magnet hen the called party responds the relay 315, being marginal, opcrates and opens the circuit of magnet 313, which deenergizes and passes the side'switch into position l. In this position the relay 306 is maintained energized by a circuit leading over arm 805 tothe grounded conductor 303. As side-switch arm 318 leaves position 8, the circuit for relay 317 is broken, but being slow to release said relav holds its armatures for an interval subsequent to the arrivaloi arm 830 in position 4. This causes an impulse to be reverted to the first selector over the following circuit: grounded lefthand armature and contact of relay 317, side-switch arm 330 (fourth position), conductor 302, terminal 218, brush 213, sideswitch arm 227 (third position), upper armature and back contact of relay 210, lower righthand winding of repeating coil 20 1, relay 233, to battery. Relay 233 closes the -following circuit for the first selector GH('L1 )Cl1li-llil n gnet 210: grounded a ature and contact of relay 233, conductor 23 sideswitch arm 215 (third position), left-hand armature and contact of magnet 206, magnet 216, to battery. The escapement magnet energizes, and as soon thereaiter as the slow relay 817 retracts its armatures to open the momentarily closed circuit of relay 233, said escapement magnet again deenergizes to escape the side switch to position Upon the sideswitch arms 227 and 235-reaching position #1, a circuit is closed for relay 233, traceable from battery, winding of said relay, lower right-hand winding of repeating coil 20%, upper armature and back contact of relay 210, side-switch arm 22'? (fourth posi tion), brush 21S, terminal 218, conductor 302, side'switch arm 332 (fourth position), brush 311, terminal 320, over the loop of station 300, terminal 319, brush 310, sideswitch-arm (fourth position), conductor 301, terminal 217, brush 212, side-switch arm 235 ("fourth position), upper right-hand winding of coil 2041, to ground.

The relay 233 thus energizes in series with. the called line, and operates to close a circuit tor the trunk connecting relay 202 at the incoming end of the inter-ofiicc trunk circuit 101, 105. Such circuit leads from grounded armature and contact oi? relay 22.; conductor 234:, left-hand winding of re a 208, winding of relay 202, to battery. lay 202 by attracting its armatures serves to remove the connection of trunk conductors 104C, 105 with the windings of repeating relay 200 and to connect said conductors directly to the left-hand portion of repeatiiug coil 20 1. The source of current ted to conductors 104, 105 from the repeating coil 2041 now flows in the proper direction for energizing polarized relay 121. Relay 121 accordingly attracts its armature and closes a circuit from battery, armature and front contact of relay 121., winding of relay 112, to ground at the right-hand armature of relay 107 Relay 112 energizes and locks up over a circuit extending from battery, upper armature and front contact of relay 112, winding of relay 112 to ground as before. By the attraction of both the armature of relay 121 and the upper armature of relay 112, the previously traced low resistance path from battery through the left-hand windings of relays 113 and 111 to ground at the upper right-hand winding of repeating coil 115 is now opened. This causes an increased flow of current through the supervisory relay 117 and trunk connecting relay 119 in the circuit hereinbet'ore described. Relay 117 energizes and closes a circuit for the called supervisory lamp 120, which is displayed to inform the operator that the called party has responded. Relay 119 by attracting its armatures electrically connects the trunk 105 to the operators cord circuit. When relay 200 was disconnected from conductors 10 1 and 105 by the relay 202 the circuit for relay 205 was at the same time opened. This relay being slow, however, does not deenergize until relay 280 has time to operate to close a holding circuit therefor. Premature release of the switches is thus prevented. The connection is'now complete for conversation.

After conversation is finished the called subscriber by replacing his receiver opens the above traced circuit for relay 233. This relay in turn causes the de'e'n rgization of trunk connecting relay 202, which disconnects the trunk 10%, 105 from repeating coil a, and again connects said trunk in series with the repeating relay 200. This results in a reversal, of battery current through polarized relay 121. Consequently relay 121 becomes inert and closes at its armature and back contact, a low resistance path from battery to ground as above traced in parallel with the circuit over which called supervisory relay 117 at this time being energized. This short circuit around relay 119 and 117 causes a sufficient reduction in current to permit their deenergization, the former relay opening the outgoing end of the trunk 10%, 105, and the latter relay serving to extinguish the lamp 120. The operator, thus being informed that conversation is finished, removes her plug 102 from the trunk jack 103. Restoration of the switching mechanism thereupon takes place as already described. i

It will now be assumed that a subscriber at an automatic substation, as substation 110, belonging to the first exchange desires to converse with the subscriber at substation 300. Upon the removal of the receiver at substation 110, the calling line lo connected in a well-known manner, as by n ot a line switch 127, 134 to a irunlr leading to an idle selector switch whose brushes are shown at 128, 129 and 180. The subscriber now operates his dial 131 to position the selector brushes 128, 129, 130 in operative relation to the terminals of trunks, such as terminals 132, 133 and 109 oi trunk 104. 105, leading to the distant exchange to which the called line belongs. The selector then. proceeds to automatically test the terminals 109 and in the well-known manner brings brusl 128, 129, 130 to rest in connection with. tl e first idle trunk found. The following circuit is now closed for stepping; relay 111: battery, upper armature and back contac 1 relay 112, left-hand windings o1 relays 1'25 and 111, contact 135, terminal 132, hrush 128, brush 12?, over the loop of so .ticn 110, brushes 134 and 129, terminal 1%, relay 136, contact 187, right-hand winding oi? relay 111, to ground. Relay 1% clo ,s an energizing circuit for the supervisory relay 107, which completes a circu t for lamp 108. The operator is thereby ii ncd that the trunk 104, 105 is engaged and will not attempt to make conncc ions with the same by means of her cord circuits. The steppii relay 111 attracts its armature and closes bridge, includingpolarized relay 121, acr the trunk conductors 104 and 105 to the repeatingrelay 200 at T-d a; change. This circuit is precisely tic same as that traced in connection with an ope fators call, the direction of current flow l) such as not to affect the pole. ized relay 1 By manipulating his dial 1.31 the su scribcr at substation 110 causes the sin.

ping relay 111 to vibrate its armature in a manner similar to that alreat y desciiocd in connection with the operas 1 of the open ators calling device 123. At each such intcrruption of the callingline, the relay 136 retracts, but relay 107 bein slow to release does not have time to de ergiae to etlace lamp 108. From this point on, the operation of stepping relay 111 under the control of the calling; subscriber se to bring about the operation of the first and nal selectors at the called exchange, and i3, has already been explained. Vfhen the called party responds and the trunk connecting lay 202 is perated to telepnouically connect the incoming end of trunk 104, 1055 to the ca]led line,'a current reversal results as fore, and polarized relay 121 now becomes energized. Relay 121 completes the circuit from its armature, through winding of the trunk connecting relay 112, to ground at relay 107. Relay 112, on acting, locks up over its own armature and connects the outgoing;

iiig line. A complete through telephonic connection is now established from the calling line in the first exchange to the called line in the second exchange and conversation may take place.

Since the system disclosed, illustrating the features oi". this invention, comprises one in which private branch exchanges are equipped with inter-exchange trunking; "'acilities it is desirable that certain provisions be made to insure a high grade of transmission for-this class or work. To such an end, means about to be brieil described are provided whereby an operator or a dial station subscriber of one exchange is not able to seize a trunk leading to a second exchange for the purpose of calling; the operator thereat, or for calling the central o'l lice. Considering this feature more 55139211 5- cally, it is to be noted that the selector switches at eaclrenchange, such as the switch shown in Fig. 2, which are used only in extending calls incoming from a distant ex change, are mounted on the multiple frame with the regular selectors which serve local subscribers lines. Therefore there appears in the multiples of the incoming switches shown in Fig. 2, trunks leading to both the exchange and central office operators. On

calls made by subscribers, individual to the exchange, the selectors therein provided to handle the local calls may be operated to extend such a calling line either to the local opcrater or to central ohicc over a direct trr i thereto by sending the proper number oi? linpulses to the switches. However, it an attempt is made by a calling line in a distant exchange to maize connection with the operator in a second exchange or to central or fice over a trunk outgoing from the second exchange by dialing this predetermined numl er of impulses, the selector, such as that shown in F 2, at the second exchange automatically restores to normal, refusing to extend such a connection. T is is accomplished by means of a wiper 23'? ca shaft 211, and arranged to wipe o group contacts during the primary movement of the switch. Consequently it it is attempted to set the brushes 212, 213 and 214 in operative relation to ljl'lllll-IS which lead, ither to the operator or to central otlice, the wiper 237 will, at the end of she primary ioveinent of the switch, so resting on one of the contacts 238. As the side switch goes to second position the following circuit is closed for the release magnet 206, and the switch returns to normal: battery, winding oi magnet 206, conductor 239, one of the coir tacts 238, wiper 211, to ground at side-switch wiper 224 (second position).

While the novel features of the present invention are set forth and describ ed in con nection with trunking system for private branch exchanges," it is to be understood that the said invention in its broader aspects is not to be limited to this particular class of work. 7

What is claimed is:

1. In a telephone exchange system, subscribers telephone lines, a trunk circuit, a connecting; circuit associated with said trunk circuit, selective switches arranged to extend said connecting; circuit to a called line, switching means for associating a call in line with said trunk circuit, means associatcd with a calling line for producing cur rent impulses, said trunk circuit being arranged to transmit said impulses over its two conductors in series, means responsive to such impulses for operating said selective switches, said trunk circuit being electrically disccnne-ted from the calling, line and said connecting; circuit during the transmission or impulses, connecting means op crated upon the response of the calledsuhscrihcr for connecting said trunk to said connecting circuit, and a second connecting means responsive to the operation of said first connecting means for connecting said line to the trunk circuit.

a telephone exchange system, sublincs, a trunl: -ircuit, a connecting; circuit associated with said trunk circuit, selective switches arranged to extend said connecting; circuit to a called line, Mitt-hing; means for associating a calling: line with said trunk circuit, means associated with the calling line for producing current impulses, said trunk circuit being arranged to transmit said impulses over its two conductors in series, means responsive to such impulses tor operatinesaid selective switches, said trunk circuit being electrically disconnected from the calling line and said connecting circuit during the transmission of in iulses, trunlr connecting relay operated in ii the response of the called subscriber for connecting the trunk so said connecting circuit. means operated by said relay for re versing the current in the trunk circuit, and a second trunlr connecting; relay responsive to such current reversal for connecting said calling line to the trunk circuit for conversation.

3. In a tel phone exchange system, suhscrihers lines, trunk circuit, connecting circuit associated with said trunk circuit, a plurality of selective switches for successirelv extending saie connecting circuit to :1 called line, operating magnets for each of sa id switches, impulse circuits for said netsswitchinp; means for associating a calling line with said trunk circuit, means associated with the calling; line for producing current impulses. said trunk being arranged to transmit said impulses over its two conductors in series, a repeating: rel ay responsive to such impulses arranged to produce impulses successively in the impulse circuits ot' the operating magnetsof eachof said selective switches, said trunk circuit being electrically disconnected from the calling line and said connecting circuit during the transmission 0% impulses, a trunk connectingrelay operated upon the response of the callcdsuhscriher for connecting the trunk circuit to said connecting circuit, means oped by said last mentioned relay for reing the current in said trunk circuit, and a second trunk connectingrelay responsire to such reversal of currenttor connecting said trunk circuit to the calling line.

In a telephone exchange system, sublines, a trunk circuit for interconnecting said lines, a connecting}; circuit associated with said trunl; circuit, selective switches arranged to extend said, connecting circuit into connection with a called line, :i 2 ching' means for associating; a calling; line with said trunk circuit, means associated with the calling line for sending:

current impulses over the two conductors of said trunk circuit in series, means itor repeating said impulses to the operating mechanism of said selective switches, said trunk circuit being: electrically d sconnectcd from the calling" line and said connecting circuit during; tl-e transmission of impul es,

a trunk connecting relay operated upon the response of the called subscriber for connecting the trunlr to said connecting Cll0fti.,t

5 means operated by said relay for reversingv the current in the trunk circuit, a polarized relay responsive to such reversal of current, and a second trunk connecting relay respons ire to the operation or" said polarized relav tor connecting said trunk circuit to the call inn line for conversation. V

In a telephone system, telephone exchanges, subscribers lines terminating in each of said exchanges, a trunk circuit leadmp; from one exchange to another, means for associating a calling line in the f rst of i said ei'zchanges with said trunk circuit, selective switches at the other exchange for extending said trunk circuit to a called line therein. means for transmitting impulses over the two conductors of said trunk in reversal of current for electrically coune ting said trunlr circuit to the calling line t'or conversation.

6. In a telephone system, a first exchange, a second exchange, subscribers lines terminating in said exchanges, a trunk circuit CIT I lective switches therein tor e outgoing from said first exchange and incoming to said second exchange, a connectmg circuit at the second or; hange, selective switches thereat for extending said conne ing circuit to a called line, sriitching means at the first ex hange for associating a callng line therein with said trunk circu' means for sending impulse from the first to the second exchange over the two conductors of said trunk in series, -eans sponsive to such impulses for ope no said selective switches, said trunl: Ci Tdlt bcilly" electrically disconnects co. ect

i rroni s l ing circuit at its incommg end and 'rrom said calling line at its outgoirq during the transmission of impulsesfa rela y operated upon the response of the called sul scriber for connecting; the incoiniiic' end oi the trunls: to said circuit, means operated by said relay for rei'ersino' the current in said trunlr circuit, and a relay the first exchange rcsponsia e to such re versal of current for connecting said trunk to the calling line. it

'T.' In a telephone sys cm, a first exchange, subscribers lines terminating in said change, a second exchange, a i'runl: circuit leading from one exchange to the other, an operator's position in the first supervisory signal at said position, switchins means at said position for associsting a calling line with the trunk circuit, a conrnecting circuit at the sccoi uch-rings, se-

circuit to a called line, means ior s impulses from the first to the sow change over the two conductors of said ti rnlr circuit in series, means in the second change responsive thereto for peratin,g said selective switches, said trunlr being el ctrically disconnected from said connectu ircuit and the calling lf during the transmission of impulses, me:ms operated upon the response oi the called su scribcr for connecting the trunk circuit at its incoming end to said connecting circuit, means oper-- ated thereupon for reversing the c rrcnt in said trunk, means operated response t such current reversal for connectir he out going end. of said trunl: to the calling line, and means also responsive to said current rcversal for operating said SUPGTYJSOJSY signal. 8. In a telephone system, a first exchange, an operators cord circuit therein, a calling line terminating; in said cord circ 0nd exchange, a called line terminating; therein, a one-Way two cond ctor trunk outgoing from the first exchange and incoming to the second exchange, means for associating the operators cord circuit With said trunk, a supervisory signal at the operators position, selective switches at the second exchange for extending the incoming; end of said trunk to the called line, means for sending impulses from the first to the second exchange over the two conductors of said trunk, means responsive to such impulses for operating said selective switches, said trunk being disconnected from the cord circuit during the transmission of impulses, means operated upon the response of the called subscriber for reversing the current in said trunk, a polarized relay operated by such current reversal, means responsive to the operation or said relay for connecting said trunk to the operators cord circuit for conversation, and means also responsire to said relay for operating said supervisory 9. lo a telephone sys em, two exchanges, a two-condor 17 trunk outgoing from one o he. incoming to the other, means O ipulses over the two conducors or? said trunk from one exchange to th ier, means at the incoming end oi said inli responsive to such impulses for e1-:- tending the same to a called line, said trunk being open at its outgoing and incoming e1 ls during the transmission of impulses, means operated upon the response of the called subscriber for closing said trunk at its i coining end and for simultaneously reversing the current therein, and means operated in resoonse to such current reversal for closing the outgoing and of said trunk for conversation.

min a telephone subscribers lines, an operators posi ion, a supervisory signal there t, a trunk circuit terminating at one end cet'ore said operators position, a selem i switch at the other end of said "us at the operators position for means ior sending impulses over said trunk, means responsive thereto for operating said switch to :rtend said trunk to a called line, said trunk beiitig; open at both ends during the transmission of impulses, means operated by the response of the called subscriber for closing both ends of said trunk for conversation and for reversing, the current therein, and means operated in response to such current reversal for displaying said signal.

11. In a telephone system, a manual subscribeus line, an automatic subscribers line, an outgoing trunk line, an operators position, means at said position for connecting the manual suhscrihers line to the outgoing end of trunk, an automatic switch for connecting the automatic subscribers line to the outgoing end of said trunlgtwo signals at the operators position, a relay, means for operating said relay when either of said. subscribers lines is connected to said trunk, means controlled by said relay for operating one of said signals and for rendering the trunk lousy at said automatic switch, a called line, means for extending said trunk to the called line, and means operated by the response to the called subscribers for rendering efi'ective the other of said signals.

12. In a telephone system, a manual subscribers line, an automatic subscribers line, an outgoing trunk line, an operators position, means at said position for connecting the manual subscribers line to the outgoing end of said trunk, an automatic switch for connecting the automatic subscribers line to the outgoing end of said trunk, a signal at the operators position, a relay, means for operating said relay when either of said subscribers lines is connected to said trunk, and means controlled by said relay for operating said signal and for rendering the trunk busy at said automatic switch.

13. In a telephone system, a manual subscribers line, an automatic subscribers line, an outgoing trimk line, an operators position, means at said position for connecting the manual subscribers line to the outgoing end of said trunk, an automatic switch for connecting the automatic subscribers line to the outgoing end of said trunk, a signal at the operators position individual to said trunk, a relay, means for operating said relay when either of said subscribers lines is connected to said trunk, means controlled by said relay for operating said signal and for rendering the trunk busy at said automatic switch, means for sending impulses over said trunk when either ofsaid lines is connected thereto, and switching means at the other end of said trunk responsive to said impulses.

In witness whereof, I hereunto subscribe my name this 19th day of March, A. D. 1918.

ALBEN E. LUNDELL. 

